Any stuttering you experience is not related to having either your game files or OpenMW on a SSD or not. A SSD simply leads to a reduced loading times, not an actual performance boost.

Actually there are certain things (e.g. sounds, random creature spawns and scripted events) that we don't preload because they're hard to predict, so using a slow drive can lead to momentary framedrops as things are loaded in. That doesn't happen very often, so it'll be more of a 'microstutter' than a noticably reduced framerate. Using an SSD will alleviate these framedrops (aside from reducing the chance of something not being preloaded on time, which can also lead to framedrops and/or waiting time). If you don't have an SSD, you can put files on a ramdisk (assuming they fit in RAM) to make things faster.

There could be a small benefit in loading time to putting OpenMW itself on an SSD as well, but that will only be relevant during game startup and never in-game. In any case, the game files will make a much larger difference.

Actually there are certain things (e.g. sounds, random creature spawns and scripted events) that we don't preload because they're hard to predict, so using a slow drive can lead to momentary framedrops as things are loaded in.

Okay, acknowledged - thanks for the correction, I have yet to grasp the whole flowchart of the source.